Saturday, January 7, 2012

Making maps from open-access data in New York - Software

Once in a while, I have the urge to draw a map of something. For instance, I wanted in my last post to include a map of the trails we took, to show where some of the interesting bits were. Because I do the odd map from time to time, I've been looking into the availability of software and data for doing them. It used to be that map-making was either done laboriously by hand on a light table, or else involved shelling out massive sums of money for software, for data and for Geographic Information Systems (GIS) consultants. But the world has improved; here I'm making notes about what I'm finding out, partly as an aid to myself because I don't do it often enough to remember where all the pieces are.

I'm a well-known cheapskate: I hate paying a lot for software and data that I'm going to use only intermittently. But I also do respect copyright. In particular, I'm surely not going to scan in a NY/NJ Trail Conference map: producing their maps is a lot of work, and selling them is one of the few sources of revenue that the Conference has to maintain the trails (short of actual donations).

Moreover, I'm working on a few things for which good maps simply don't exist. One example is that my community has several rather nice nature preserves. One in particular, the former Schenectady Museum Nature Preserve, transferred to New York State a few years back. It's now an unnamed and unsigned parcel of parkland, that the state really doesn't quite know what to do with. But the footpaths in it still exist and are regularly used - and a few people are even maintaining them.

But the available maps of the preserve don't quite agree with one another, and they vary in readability and completeness. The three that I've found on line are here, here and here. I don't think any of them is entirely satisfactory as it is. To begin with, the only one that actually shows the land boundary and the blaze colors fails to show any context and lacks contour lines. Surely I can do better.

So, let's see what's out there. I got inspired by stumbling upon a post by Andy Arthur introducing Quantum GIS for making trail maps. His end result was reasonably attractive, and the program looked useful, so I decided to give it a shot.

Like many things in the open-source world, the program's distribution is a bit chaotic. There are a lot of pieces with "some assembly required," at least under Debian and related systems such as Ubuntu. Material that I know was needed included QGIS itself, GDAL and QGIS's GDAL Python tools, PostGIS (we'll come to why I wanted that in a later post), which in turn requires the Postgres 'contrib' repository and a package called 'hstore', and Postgres itself, and a number of other minor bits. Many of these are components that are run-time loaded into QGIS, and need compatible versions of client libraries (libtiff 3 versus libtiff 4, PostgreSQL 8.4 vs 9.1, and so on). I managed to get something patched together just before giving up and trying to build the whole shebang from source. We'll see whether the next run of the update manager brings everything crashing down around me.

Once everything installs, the program looks pretty good. The UI is professional, and the functionality all seems to be there. Now for getting some maps! Fortunately, in New York, data availability is quite good. In the next post, I start trolling for data.
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